Brake talk again.

[oscar]

my partner would pump up a good hard pedal while I let off the nipple and then tightened it up at midstream so the pedal never floored.

Interesting you mentioned the pedal was never floored WGB.

I've still yet to do anything further on the brakes, just haven't had time.  I've thought long and hard about the booster chinny and Craig.  I'm definitely tempted to swap it for another one but I find it hard to fathom that something faulty with it could cause the pedal to move further than it should or sink. ie if there was no air in the system and the MC doesn't leak internally, the booster seems mechanically connected to the MC's piston and the fluid shouldn't compress any further.

My only thought that I had ages ago related to the booster's input shaft and output shaft which are kind of connected physically but are separate parts.  Pulling or pushing on one side affects the other but another part or few parts connect them but not rigidly.  So I was thinking that with vacuum and pushing hard on the pedal it causes one of these shafts to become skewed and off centre the harder you push with vacuum.  Maybe a stretched weakspot off centre in the diaphragm has developed and only materialises with vacuum and causes misalignment of the two shafts in the booster.  The sinking is like the two shafts are nearly sliding past each other with the membrane in between stretched... kinda sorta know what I mean   need to pull a spare apart.

Above all though, I really need to try the bleed method where the pedal doesn't touch the floor before I start dissecting things.

[WGB]

Hi Oscar,

In an older car there is an advantage in not forcing the master cylinder through it's full stroke and that is to prevent the rubber seals from passing over any corroded area in the furthest end of the cylinder and becoming damaged.

As Koan has said in the past if the master cylinder is that bad it should be replaced but if all you want to do is a fluid change it will put off the inevitable rebuild day.

There is also no need to do this if you have a reasonable pedal as you only have to  pump up the pressure and then release it half way with the person turning the bleed nipple controlling how far the pedal goes down.

It's the pressure after the pump up followed by the short sharp flow that presumably dislodges the trapped bubbles.

I was planning on a complete rubber replacement of my 6.9 brakes this summer but as they are working perfectly and I have a good pedal all this talk of spongy pedals is starting to give me cold feet.


Bill

[Takernz]

pardon me for crashing in your post, Can I install a later W126 brake rotor b/c it's wider than standard W116 rotors, and this swap can improve braking performance in all driving conditions?

[s class]

pardon me for crashing in your post, Can I install a later W126 brake rotor b/c it's wider than standard W116 rotors, and this swap can improve braking performance in all driving conditions?

What do you mean wider?  Do you mean thicker, different offset, or larger diameter?

And in anycase, I'm of the opinion that once a W116 braking system is sorted, it is more than good enough. 

[Big_Richard]

early and late w126 use the same steering knuckles as 116, so yes, you can fit 126 front brakes to a 116, but you must replace both the calipers and the disks as a set as neither are interchangeable with w116 parts.

i have new 116 calipers and disks on my 116 w/ stainless brake hoses and the braking is phenomenal, firm, very responsive brake pedal. Still using the original master cylinder, although with a new tank & grommets. 126 upgrading will achieve little over a well sorted 116 system.

[Big_Richard]

re the stainless hoses, i for the life of me cant remember where i purchased them from, they were a custom order from a Canadian company.

as far as I'm aware, no one has them on the shelf, due to the 2 different version w116 rear ends, anti-squat versus low spec, they use different hoses. As such no one wants to take the gamble of providing the wrong version.

custom will be the only way anyone can ever get these hoses.

[WGB]

If you are fitting 126 brakes you might need to check wheel clearances with 14 inch wheels as well as Master cylinder to Caliper hydraulic bore diameters.

It is quite economical to refurbish 116 brakes and I am not sure anyone would get any noticeable braking improvement using 126 parts .

There may even be a small possibility of a missmatch between  hydraulic components.

New 116 discs are less than $100 EACH.  Pad sets are not expensive and I have just ordered a complete set of rubber brake parts including new master cylinder, fluid reservoir, hoses and kits for all calipers for less than US$300.

If you want to race it go Brembo buyt he only real street improvement would be ABS but that would require a lot of work.

Bill

[craigb]

I agree for the road my 116 brakes are great but on the track with slightly higher temp pads they are boderline. Ian and Cam get good results using a track pad and standard brakes and I am sure if I went QFM k 750 or maybe EBC yellow it might well fix the problem - I have a six and the others are 8's. If I was continuing to do track work and wanted to drive to the track, for the cost involved I would go better pads but also the late W126 brakes. In Oz RDA slotted rotors (that help get rid of gas at fade point) are less than $100 and I picked the calipers up from a wrecker for $40 I think it was. Kits are cheap. Early W126 is the same on the sedans and coupe brakes are probably not that easy to find, and the late ones are better than that. I am just in the process of putting the late brakes on my gen 1 W126 coupe. Although the pad size is the same, they are 300mm rather than 278mm diameter but under continued hard braking they have a much wider ventilation gap. They will bolt on but you need the calipers. If you have the later W116 and 6.9 master, then that works with them. But with that diameter you do need 15" plus wheel size. And any post 85 W126 has the same bigger brakes from 300 to 560.
Lastly on brake lines, there is a place in Adelaide "Power Brakes" that will make up any braided line for $70 if that is of any interest. Postage would be cheap enough but depending where you are, no doubt someone local will make them too. I haven't gone down that road but I am suspect of the rubber performance when it is really hot, even though they are new lines..... but that is another story and it is getting late!

[Takernz]

yes, sorry thicker not wider , anyway, here in the Philippines the front brake caliper is getting harder to find here and worst thing  is, unique to the W116 ( e.g. W123 calipers is different to W116 so is the W126) about 20 years ago they're plenty. My 280S's front right caliper is leaking fluid in the center where the halves are joined. The manual says that the calipers are cannot be broken apart, but I ignored it and proceeding in breaking the calipers in 2 halves and I found 2 small O-rings about 4mm in diameter, I ran into a store that specializes O-rings and hydraulics and they came up with a VITON one but has circular in cross-section(originals had square cross-section), and I  bought 2 O-rings but a little fatter, assembled the caliper , installed in the car, placed a piece of table napkin on top of it and  bled and checking for leaks if the napkin is wet, unfortunately it did wet, it was leaking again,and the caliper is shot. Also I changed brake booster 3 times!! but all of them are used, new ones cost me about US$750 for a W126 booster not W116, but they're the same anyway.


My long-time parts dealer of mine says that I had to convert my existing front brakes to W126 b/c not only plenty and swappable but it will perform better than the original one, and slotted discs and stainless steel braided brake hoses would be great but how can I get it? how much does it cost(for all hoses)? Is slotted discs are good for street use? I just want a reliable brakes since I almost encountering an accident due to weak brakes even with busted booster!.

As to chinny, what is your car? If your car is petrol, start the car and begin depressing the brakes and listen for hissing sound and the engine idles like crazy, if it is, you have a busted booster for diesel, check first the vacuum pump to see if the diaphragm was not ruptured,and for the budget conscious like me, I wanna go for used one. I bought a used one(3rd and current booster) out from wrecked W126 for US$100! I was lucky b/c the booster was less than 2 years old according to the owner of wrecked W126.

[Big_Richard]

i had slotted and cross drilled brakes on my "other" car, yes they do perform well in extremely abusive conditions - theres zero brake fade and they stop the car very well all the time without fail.

on a daily driver though, the fact that they act like a cheese grater on the pads means they require much more maintenance. Pads aren't expensive but its just more work to do... I was changing all 4 corners pads every 10,000 service on my daily driver.

if 126 calipers and disks as a set are plentiful, change them over, they bolt straight on.

[craigb]

It was suggested to me not to run drilled rotors but just slotted. Reasons were cracking common, less contact area and wear, although in extreme circumstances they do have a place. Also unless you are on the limits of fade, my understanding is the slots will do nothing for your performance - they just vent gas at extreme levels. You will get a lot more out of a good pad than out of a slotted disc.

And just a comment on the rears, you will find the rear caliper and pad size is the same from a W108 6cyl right through to a late 560 W126. I wear my fronts at least double the rate of the rears with combined track and commuting, and an engineer mate reckons that is about right. So I would only worry about the performance of the fronts.

Takernz, I think you will find that pre 85 W126 calipers are the same so I don't know what their availability is like. Certainly online catalogues suggest same. Post 85 is bigger as discussed.

As for the orings, I just picked up caliper rebuild kits and they include normal round orings. I think what square profile has been formed from years of being jammed in there and I would expect that to occur. I am surprised that didn't fix your problem 0 are you sure the new ones were big enough? they are under a lot of pressure and as you can see the old ones got so squashed they filled the cavity as a square.

And for your lines, I reckon standard are fine for normal useage (just my opinion) and you can get them for about $10 from autohaus.az and if you are keen on braided, you could contact these people for a quote:

http://www.powerbrakes.com.au

[TJ 450]

Early W126 brakes will fit a W116, but you have to change the rotors and shields as well. The offset is different. I have W126 Bendix front brakes on my 6.9.

I will be fitting the post '86 w126 big brakes on my 380SE, so I will find out if the 14" wheels still fit, which isn't likely. I may end up refitting the 16" Centra wheels on the car if the bundts don't fit.

Tim

[Takernz]

from what I'm reading here from you folks, I prefer 2nd gen W126 b/c they're bigger than 1st gen, but as what craigb and tim has said, fitting that with 14 inch wheels is a big question, but a friend of mine offered me a rare set of AMG Penta wheels (made by ATS), the size is 6.5JX16 for US$400. That will answer the question but I have to save some more to buy that wheel and the 2nd gen W126 front brakes as well, (I have to sell my 14-inch Centra wheels currently on my car and a pair of W116 front disc, if necessary).

As for the pads, ATE, PAGID and TEXTAR are plentiful here and they're standard on all W116s, I find the PAGID better b/c a bit softer, they brake well when cold but they wear a bit faster than the other 2.

[craigb]

thanks Tim, that's good to know about the offset. I was just going with data I had gleaned.

Do you know why the change of offset? Just wondered if there was any logic to it?

[TJ 450]

I'm not sure why the different offset. In fact, PB discovered this difference when he went to fit the W126 calipers to his 6.9.

But yes, the rears are all the same.

Tim